Controllable electric discharge tube operating with alternating current



A. ETZRODT E ELECTRIC DISCHARGE TUBE OPERATIN WITH ALTERNATING CURRENT Filed July 6, 1939 May 22, 1941;

' CONTROLLABL Patented May 20, 1941 CONTROLLABLE ELECTRIC DISCHARGE TUBE OPERATING WITH ALTERNAT IN G CURRENT Adalbert Etzrodt, Berlin-Siemensstadt, Germany, assignor to Fides Gesellschaft fiir die Verwaltung und Verwertung von gewerblichen Schutzrechten mit beschrankter Haftung, Berlin, Germany, a corporation of Germany Application July 6, 1939, Serial No. 283,036

, In Germany June 23, 1937 6 Claims.

This invention relates to a controllable electric discharge tube operating with alternating current and in which the flow of the current is made possible in two directions by the fact that two correspondingly designed electrodes alternately operate as a cathode and an anode respectively. As cathodes hollow cathodes are, as a rule, employed, in which, for instance, a helical filament is placed within a shielding member provided with an aperture for the passage of the electrons, By correspondingly arranging the control elements the moment at which the ignition of the discharge occurs in each direction may be determined so that the mean current intensity of the alternating current flowing through the tube is regulated. Accordingly, the tubes are particularly suitable for regulating purposes; i. e. for all fields of application where a change of the efiective value of the alternating current is necessary and for which, in general, two tubes connected in opposition had to be hitherto employed.

The above-described tubes present, however, certain drawbacks which restrict their fields of application. In practice, it has been found that the cathodes of such tubes and consequently the tubes themselves have not such a long life as would be desirable. Furthermore, the tubes hitherto employed present the disadvantages in that it is not possible to control the current intensity in an absolutely reliable manner by applying certain potentials to the control grid or.

grids.

The object of the present invention is to avoid the above-mentioned drawbacks.

In a controllable electric discharge tube operating with alternating current and provided with two electrodes which alternately serve as an anode and as a cathode, each of the two electrodes consists according to the invention of an electron emitting part, for instance, an activated helical filament, and of a shielding part enclosing the electron emitting part and which acts as an anode when the electrode is impressed with a positive voltage, these two parts being, for instance, thermally isolated from each other by shields or by poor heat conductors arranged between these two parts. The invention is based on the following fact: Each hot cathode is designed for a predetermined temperature at which it has the longest life. Consequently, the temperature must lie within certain limits. If now the heat developed by the discharge of the electrode part operating as an anode influences the temperature of the cathode as a result of the conduction or radiation, the temperature is no longer defined and the cathode often operates under unfavorable conditions so that the life of a tube is considerably reduced. Another drawback of the varying cathode temperature consists in the fact that the moment at which the ignition occurs for a. predetermined grid potential is dependent upon the power in the case of a transfer of heat between the cathode part and the anode electrode part. For this reason the two electrode parts are so thermally isolated from each other as to remove the above-mentioned drawbacks.

In the accompanying drawing are shown some forms of the invention in diagrammatic form.

As shown in Fig. 1 an electrode system is provided at both ends of the discharge path, each system'consisting of a hot cathode I, a shield 2, and a further shield 3. In the discharge path are further arranged two control electrodes 4 and 5. Depending upon the potential with which the two control electrodes are impressed, the moment at which the ignition occurs may be adjusted at will, The shield 2 prevents a direct radiation of heat from the anode 3 to the oathode I. be improved to a further extent it may, for instance, be designed as shown in Fig. 2 in such a manner that it completely protects the shield 6 which serves as an anode against the spiral filament I.

In Fig. 1 is also shown in diagrammatic form a connection in which the tube may be operated according to the invention. The current consuming device I3 is supplied by the source I2 with an alternating current whose eifective value is controlled by the discharge tube. The control voltages for the two control grids are produced by a control device I4. .15 and It denote heating current sources for the two hot cathodes of the discharge tube.

In order to attain a still better action of the shields a hollow cathode (Fig. 3) consisting of a helical filament 8 and of a shield 9 may be employed, the hollow cathode being surrounded by another shield Ill, which in turn is enclosed by a shield H serving as an anode. It has proved advantageous to blacken the outer surface of the shield II and to polish its inner surface. Also the inner and outer surfaces of the intermediate shield =l0 are given a glittering appearance. 'The heat of the cathode is thus intensely radiated outwardly, whereas the cathode is completely protected against the heat radiating from the anode part. In this manner there results a saving in energy required in heating up the cathode.

In case the action of the shield should i designed :to suit the particular conditions. A

single grid may be provided for controlling the discharge in both directions; however, also two or more grids may be employed.

Also the shape of the other electrodes may be chosen to meet the particular requirements. In

this case it is essential that the two parts .be- 1 longing to each electrode; i. e. the partacting as an electrode producing source be always thefmally isolated from the part acting as an anode.

What is claimed is: 1

1. In an electron discharge tube adapted to pass alternating current, a cathode and anode at one end of the tube, a cathode and anode at the other end, each cathode being included in a discharge path with the ano'de associated with the other cathode, means for shielding each cathode against the transfer of heat from the adjacent anode, and supports embodying low heat conductivity material thermally insulating said cathodes from said means.

2. In an electron discharge tube adapted to pass alternating current, two pairs of electrodes,

each pair comprising a cathode and anode, said pairs being arranged opposite each other so as to provide a discharge path from each cathode to the opposite anode, grid means for controlling said paths, means for shielding the cathode of each pair against the transfer of heat from the associated anode, and supports embodying low heat conductivity material insulating each cathode from its associated means for shielding.

3. In an electron discharge tube adapted to pass alternating current, twopairs of electrodes eachvcomprising. a cathode and an anode, said pairs being arranged opposite each other so as to provide a discharge path from each cathode to the opposite anode, means for heating each cathode to a desired temperature, shielding means for each cathode to prevent an objectionable rise in its temperature due to heat transferred from the adjacent anode, and supports embodying lowheat conductivity material thermally insulating each cathode and its associated shielding means.

4. In ,an electron discharge tube adapted to pass alternating current, two cathodes disposed opposite each other, an anode surrounding each cathode, a shield arranged between each cathode and its surrounding anode to prevent heat radiation between them, aligned openings in each anode and the associated shield to provide a discharge path from the enclosed cathode to the opposite anode, each shield being insulated from its associated cathode.

' ,5. The structure as claimed in claim 4, in which the shields have a polished surface on one side. 6. The structure as claimed in claim 4, in which the anode surfaces are designed to radiate heat outwardly more readily than inwardly.

ADALBERT ETZRODT. 

